SUMMARY Timeline navigation becomes noticeably slow when the number of clips reaches ~800 or more. Scrolling and zooming the timeline lag, making editing uncomfortable even without effects, transitions, or animations. STEPS TO REPRODUCE 1. Create a project with long footage (e.g. ~1.5 hours) on two video tracks with two synced audio tracks. 2. Perform extensive cutting to remove unwanted parts until the timeline contains ~800–1000 individual clips. 3. Try scrolling horizontally and zooming in/out on the timeline, especially during playback. OBSERVED RESULT - Timeline scrolling becomes sluggish. - Timeline zooming lags and feels delayed/step-based. - While playback is running, scroll and zoom responsiveness degrades further. - The UI remains functional, but navigation becomes uncomfortable and slow. - System resources (CPU/GPU/RAM) are not fully utilized. EXPECTED RESULT Timeline scrolling and zooming should remain responsive with hundreds of clips, especially during basic rough-cut workflows without effects or compositing. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Ubuntu 24.04 (Wayland, GNOME) KDE Plasma Version: N/A ADDITIONAL INFORMATION - I will provide a download link to the project file so the issue can be reproduced directly. - Actual Kdenlive version: 25.11.70 - Project link download: https://drive.google.com/file/d/1bXhkKy3dZVdrqdJYDd5acxvI1uIT6S2F/view?usp=drive_link